1. Field of the Invention
The present invention relates to an exhaust gas control valve for controlling the quantity of exhaust gases to be recirculated in order to minimize the noxious (or toxic) emission, especially the nitrogen oxides (NOx) emission from an internal combustion engine.
2. Description of the Prior Art
There has been known an exhaust gas control valve which is operated by a diaphragm which in turn is deflected in response to the negative pressure transmitted through a port opening slightly upstream of throttle valve in a carburetor so that the flow rate of exhaust gases to be recirculated may be controlled in response to the operating conditions of an internal combustion engine. However, in the exhaust gas control valve of the described, the flow rate of exhaust gases to be recirculated is controlled only in response to the opening degree of the throttle valve so that the quantity of exhaust gases to be recirculated is less when the engine is running under the heavy load, resulting in emission of a large quantity of nitrogen oxides (NOx). As a result, the NOx emission cannot be reduced to a satisfactory degree. On the contrary, if the exhaust gas control valve of the type described is so arranged as to recirculate a large quantity of exhaust gases under the heavy load, the sufficient engine output cannot be obtained at low speeds so that the engine operation and the driver's feeling of the engine operation may be badly affected.
In order to overcome the above problems, there has been devised and demonstrated an exhaust gas control valve of the type having two diaphragms which are subjected to two different negative pressures (for instance, the negative pressure in the carburetor and the negative pressure of the intake air). However, the use of two diaphragms not only results in the inevitable increase in cost but also places the limits on the size (especially in the longitudinal direction) of the exhaust gas control valves which must be as compact as practicable as they are mounted on the automotive vehicles.